Magnetic resonance imaging (MRI) techniques have been widely used in a broad range of medical and biological studies and diagnoses. The conventional MRI is based on a mechanism of contrast in relaxation time (T2) for nuclear magnetic resonance of a proton in a biological specimen due to interaction between the proton and any adjacent magnetic contrast agents. The sensitivity of conventional MRI is seriously limited due to the small population differences Δn in two adjacent Zeeman levels governed by Boltzmann statistics:                                           Δ            ⁢                                                   ⁢            n                    =                      1            -                          exp              ⁢                                                           ⁢                              (                                  -                                                            h                      ⁢                                                                                           ⁢                      v                                                              k                      ⁢                                                                                           ⁢                      T                                                                      )                                                    ,                            (        1        )            where h is Plank's constant, and v is magnetic resonant frequency, which is related to external magnetic field B by the following equation:hv=g μB,  (2)where g is gyromagnetic ratio, μ is the nuclear magneton μN for nuclear magnetic resonance (NMR). At room temperature and in a 5 Tesla magnetic field, this corresponds to a factor of 10−5 reduction in sensitivity for a typical NMR, and therefore for MRI. Because the mass of an electron is about 1863 times smaller than the mass of a proton, in electron spin resonance (ESR), μ is replaced by Bohr magnetron μB and the spin population difference is only 10−2 at room temperature in a 5 Tesla magnetic field. However, the required frequency for electromagnetic radiation to excite the spin resonance, typically 9.8 GHz, is much higher than that of NMR. Radiation having this frequency cannot penetrate deeply and suffers large dielectric loss in a biological specimen, rendering the technique useless in MRI imaging. Recently, many efforts have been made to use lower frequency ESR technique (200 MHz to 3 GHz) for MRI. What is needed is a reliable technique for perfoming MRI at lower frequencies, preferably no more than 1 GHz.